The present invention broadly relates to gear cutting machines and, more specifically, pertains to a new and improved construction of a gear cutting machine for cutting spiral bevel gears and contrate gear face clutches according to the continuous gear-cutting process.
Generally speaking, the gear cutting machine of the present invention is for cutting spiral bevel gears and contrate gear face clutches having cycloidal tooth flank lines or generatrices according to the continuous gear-cutting process and comprises a rotary first spindle for mounting a cutting tool or gear tooth cutter, a rotary second spindle for holding a workpiece or gear blank, a primary drive train operatively interconnecting the first and second spindles and having a termination at the second spindle, and a reversible main drive means operatively connected to the primary drive train for simultaneously driving the first and second spindles.
A first method of the present invention is for cutting spiral bevel gears and contrate gear face clutches having hypocycloidal tooth flank lines or generatrices according to the continuous gear-cutting process by means of a gear cutting machine according to the present invention. A second method of the present invention is for cutting spiral bevel gears and contrate gear face clutches having epicycloidal tooth flank lines or generatrices according to the continuous gear-cutting process by means of a gear cutting machine according to the present invention.
Methods for cutting bevel gears with curved teeth according to the continuous gear-cutting process are known, such as for instance, the method known from the Swiss Patent No. 271,703, published Feb. 16, 1951. According to this known method the eccentricity of the gear tooth cutter axis in relation to the main axis of the machine can be determined according to various formulae for mutually identical and mutually opposed directions of rotation of the gear tooth cutter and for an idealized contrate gear. Gear tooth cutters are also disclosed for which the magnitude of the orientation or set-up angle of the cutter blades of the gear tooth cutter can also be determined from various formulae for mutually identical and mutually opposed directions of rotation of the gear tooth cutter and the contrate gear.
It is thus known that gears which have epicycloidal gear tooth flank lines or generatrices can be generated according to the continuous gear-cutting process by rotating the workpiece or gear blank and the tool or gear tooth cutter in mutually opposed directions of rotation. This procedure is also known as counter-cutting or counter-milling. It is likewise known that gears having hypocycloidal gear tooth flank lines or generatrices can be generated according to the continuous gear-cutting process by rotating the workpiece or gear blank and the tool or gear tooth cutter in mutually identical directions of rotation. This procedure is also called forward cutting or climb-milling.
However, only counter cutting based upon the generation of an extended epicycloid has prevailed in practice for fabricating bevel gears according to the continuous gear cutting process. Tool or gear tooth cutter spindles and workpiece or gear blank spindles are mechanically coupled by a transmission or drive train and driven by a single motor in mutually opposed directions of rotation. In order to reduce chatter or backlash in the drive train during gear-cutting, which is conjointly induced by the intermittency of the cutting force or torque and play or clearances in the drive train, a braking torque is exerted upon the workpiece or gear blank spindle, usually by mechanical or hydraulic braking devices. Although this problem is controllable in counter-cutting procedures, in forward cutting or climb-milling procedures it is exacerbated to such an extent that the fabrication of bevel gears having hypocycloidal tooth flank lines or generatrices has not heretofore been undertaken.
A gear generating miller or milling machine is known from the German Patent Publication No. 1,056,453, published Apr. 30, 1959, which has a drive train or transmission between the tool or cutter and the workpiece or gear blank as well as a circular or rotary table or workpiece support fitted with a worm wheel or worm gear ring or rim. The circular table is rotatably mounted between a first worm engaging the worm gear ring and a second worm engaging the worm gear ring and driving the worm gear ring. The first worm forms a termination of the drive train between the tool or cutter and the workpiece or gear blank. The first worm serves only to enable or permit rotation of the round table without driving it, while the drive of the second worm is tapped from a power take-off point lying outside of the drive train between the tool or gear tooth cutter and the workpiece or gear blank. The first and the second worms are preferably driven by separate motors, e.g. hydraulic or electric motors.
Another machine for cutting gear teeth of gear wheels according to the generating process is known from the German Patent No. 2,611,544 and the corresponding U.S. Pat. No. 3,971,293, granted July 27, 1976. A gear cutter or cutter head spindle is mounted in a generating drum or roll cradle and driven by a first drive means. The generating drum and a workpiece or gear blank spindle are connected in temporal dependence with one another by a gear-generating drive train. The generating drum and the workpiece spindle are simultaneously driven in at least one direction of rotation by a second drive means arranged between the generating drum and the workpiece spindle. A third drive means drives the gear-generating drive train in the same direction of rotation as the second drive means and is arranged at the workpiece spindle. This arrangement maintains the gear-generating drive train under constant load during generating milling, i.e. suppresses backlash.
Known gear cutting machines for cutting spiral bevel gears having epicycloidal tooth flank lines or generatrices according to the continuous gear cutting process are grouped in model series or classes of construction type for fabricating gears ranging from small bevel gears of a few millimeters diameter to large bevel gears of several meters diameter and having epicycloidal tooth flank lines or generatrices. The range of application of these machines is determined by the diameter of the ring bevel gear, i.e. the larger of the gears of the bevel gear pair. This primarily depends upon the distance by which the gear tooth cutter or cutter head of the machine can be adjusted eccentric to the principal machine axis, i.e. to the axis of the generating drum or roll cradle. The greatest eccentricity is, in its turn, the major factor determining the generating drum or roll cradle size and is therefore a major factor in the overall dimensions of the machine. If sizes of bevel gear are to be fabricated which exceed the range of application, i.e. the working range, of a given size of machine, economical considerations such as a limited market can hinder the construction or acquisition of a correspondingly larger gear cutting machine and therefore the fabrication of such larger bevel gears.